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UNITED S'l'A'l'lf'a FA'lFld'l. QFFICE.

LUCIAN W. BUGBEE, OF INDIANAPOLIS, INDANA, ASSIGNOR T0 TWINSXGHT OIWEICAI l l i CO., OF NDANAPOLS, INDIANA.

BIFOCAL LENS AND PROCESS FR MAKING THE SAME.

Leraars.

Specification of Letters Patent.

latented May 3, 1921.

Application led August 20, 1920. Serial No. 404,770.

To all whom t may concern Be it known that I, LUCIAN WV. Bosnian, a citizen of the United States, and a resident of Indianapolis, county of Marion, and State of Indiana, have invented a certain new and useful Bifocal Lens and Process for Making the Same; and l'do hereby declare that the following is a full, clear, and exact description thereof, reference being had to the accompanying drawings, in which like numerals refer to like parts.

The object of this invention is to avoid the difficulty in polishing bifocal lenses and the danger of injuring the same at the line of joinder of the bifocal surfaces, as well as to produce a lens of the kind of good' optical qualities at low cost.

1n polishing bifocal lenses with merging surfaces, effort has always been made to avoid marring the line line of joinder created in the previous grinding or generating process and causing prismatic aberration. Such effort has made the polishing process slow and expensive, if well done, and injurious to the lens if carelessly done.

The chief feature of this invention consists in forming an annular groove or recess at the line of joinder, after the grinding of the bifocal surfaces, which enables each surface to be polished by a button or lap without danger of reaching and injuring the other surface. The margin of each surface will then be completely and well polished and the groove having an unpolished and opaque surface, will not injuriously affect the eyes y0r vision.

In the drawings Figure 1 is a plan view of a single piece of glass or blank on one side of which bifocal surfaces have been ground so as to have the desired curvatures, the near or reading portion being at the center and it being surrounded by the far or distant portion. Fig. 2 is a central section of Fig. 1. Fig. 3 is a plan view of the blank after the next step in the operation, with the annular groove ground therein. Fig. 4 is a central section of Fig. 3. Figs. 5 and 6 show portions of Figs. 3 and l on a large scale, with the central surface polishing button being shown by dotted lines. Fig. 7 is a plan view of a finished lens.

The iirststep in the process is to grind and generate the bifocal surfaces on the glass. As shown in Figs. 1 and 2 this is done by grinding a target double blank 10 saucer shaped, with the two surfaces merging with a fine line of joinder 11 between the inner or near surface 12 and the surrounding or distance surface 13. This may be done by simultaneously grinding said surface by a single tool with a plurality of generating surfaces, or by successively grinding them by suitable laps or tools.

The second step in the process is to grind an annular groove or recess 14- coincident Vwith the line of j oinder. rllhis can be easily and quickly done, but the groove should be narrow and shallow.

The third step in the process is to polish the surfaces. rThis should preferably be done by a separate polishing button or lap for each surface. ln Figs. 5 and 6 a button 15 is shown by dotted lines for polishing the central surface, and as it here appears, the polishing button can overlap the boundary of the inner or near surface 12 and project somewhat over the groove 14;, without cracking or endangering the inner edge of the surrounding or distance surface 13. Hence, the surfaces can be accurately and well polished quickly.

After the polishing is finished, the target blank in Fig. 3 is centrally cut in two to form two halves or blanks. Then the back surfaces are formed according to the desired prescription, and edged and finished to make lenses like that shown in Fig. 7.

The groove dividing the two surfaces remains in the finished lens, but its surface is unpolished and therefore it is not objectionj able to the eyes and causes no prismatic aberation, while the bifocal surfaces are perfect throughout.

By the word groove7 as used herein is meant a groove or recess substantially as shown in the drawings as distinguished over a shoulder as shown in Letters Patent to Alexander No. 954,772. Thus such a groove has two side walls. Y

By the language the surfaces adjacent the groove being on substantially the same level is meant a construction substantially as shown in Fig. 4. wherein the surfaces 12 and 13 adjacent the groove 111l have the saine relative elevation, one not being substantially higher than the other and not shouldered with reference to the other.

The invention claimed is:

1. A bifocal lens having a groove separating the visual. surfaces thereof.

2. A bifocal lens having a groove ground between and separating the visual surfaces thereof.

3. A bifocal lens blank having a central surface of one curvature, a surrounding surface of another curvature, and an annular groove between and separating said surfaces.

4. A bifocal lens having on one side two visual surfaces with a groove between and separating said surfaces, said surfaces adjacent said groove` being on substantially the same level.

5. In the process of making a bifocal lens, first grinding the bifocal surfaces With their desired curvatures, second grinding a groove along the line of joinder of said surfaces, and then polishing said surfaces.

6. In the process 0f making` a bifocal lens, first grinding the bifocal surfaces with their desired curvatures, second grinding a groove along the line of joinder of said surfaces, and then separately polishing said surfaces.

7. The process of making a bifocal lens Consisting of grinding a Central surface for near vision surrounded by a surface for far vision with the two surfaces substantially merging at their iunction, grinding an annular groove along` the line of joinder, polishing said surfaces, centrally cutting the blank into two blanks, surfacing the other sides of said last blanks, and finishing the same to form lenses.

In witness whereof, I have hereunto affixed my signature.

LUCIAN W. BUGBEE. 

